Just for clarity, Graphene doesn’t provide a “neutered” version of play services - the version of play services which runs is the same code as provided by Google, with the only difference being that it runs in a sandbox which only grants it the same level of permission as normal apps (which you can choose to grant or not) rather than running as effectively root on your device like it does on most android phones.
OP specifically said they don’t want to dual boot, and I honestly understand why they would say that.
When you dual boot you need to worry about what bootloader is in use and how it is set up. You might find yourself in a situation where you later decide to move fully to Linux and use the old Windows drive as storage but you can’t because if you wipe it then everything stops working.
Windows has even been known to destroy dual boot setups occasionally during Windows updates.
All very solveable if you have the right knowledge, but if you want to keep your life simple then swapping hardware has guaranteed safety (nothing can go wrong with the contents if a drive if it’s not plugged in, after all) and it’s very predictable and understandable.